Thin-walled structures, such as for example circularly cylindrical shells, tend to form a buckling pattern under axial pressure load, so that large deformations occur perpendicular to the direction of the axial pressure load. Such a buckling pattern can for example be formed circumferentially, which is also understood to mean a global buckling. Said global buckling patterns often arise suddenly and without prior notice, wherein the axial load-bearing capacity of the structure is significantly reduced by said deformation (buckling).
The cause of said deformation, and hence the accompanying strong reduction of the possible axial load-bearing capacity, can for example be manufacturing-related deviations in the geometry (geometric “mid-surface” imperfections MSI) or deviations from the ideal homogenous loading (geometric “boundary condition” imperfections BCD. In this case, said deviations from the geometry or the ideal homogenous loading can significantly reduce the maximum possible load-bearing capacity of a cylindrical shell, so that this is very important in the planning and development of thin-walled structures, in particular in air travel and space travel.
In the 1950s and 1960s, many buckling tests on thin-walled cylindrical shells of isotropic materials and substances, such as for example steel or aluminum, were carried out. In order to derive the design load NNASA, the non-linear buckling load Nn-lin of the perfect shell, i.e. without imperfections, is required, wherein the non-linear buckling load is reduced by a reduction factor pNASA as a function of the slenderness R/t (quotient of radius R and wall thickness t), in order to take into account the imperfections of the cylindrical shell. The design load NNASA can be calculated using the following equation:NNASA=Nn-linper·pNASA.The reduction factor is in this case the quotient of the experimental and theoretical linear buckling loads of an ideal perfect shell and decreases with increasing slenderness.